Overdue invoices Free browser tool

Calculate the balance before you chase the payment.

Apply only the written rate and fee you are permitted to use, measure the business cost of waiting, and copy a calm payment reminder.

No signupPrivate in your browserCopy-ready output

Enter the written payment terms

Use only the rate, grace period, and fee your agreement and local law permit.

CurrencyInvoice referenceOutstanding invoice amount$Days overduedaysGrace period after due datedaysInterest rate periodWritten annual rate%Example value only—replace it with your permitted written rate. The calculator uses simple daily proration on a 365-day year.Written flat fee, if any$Your annual cost of delayed cash%An internal planning rate for financing, lost return, or cash-flow pressure. It is not added to the client balance.

Overdue invoice readout

Separate the contractual calculation from the cost the delay creates inside your business.

Chargeable days45

Prorated interest$55.48

Flat fee applied$0.00

Total late charge$55.48

Updated balance$2,555.48

Internal cost of the delay$36.99

CLIENT-READY REMINDER

INV-042 for $2,500.00 is 45 days overdue. Per our written payment terms, the late charge calculated for this overdue period is $55.48, bringing the updated balance to $2,555.48. Please confirm the payment date. This calculation uses the terms already entered above; our agreement and applicable law determine whether the charge may be applied.

CALCULATION RECORD

INV-042: original balance $2,500.00 + $55.48 simple interest + $0.00 flat fee = $2,555.48 total. Chargeable period: 45 days after the 0-day grace period. Annualized rate used: 18.00%.

THE LATE-PAYMENT METHOD

Calculate what the terms say—not what the delay feels like.

An overdue invoice creates two different numbers: the charge your written terms may allow and the internal cash-flow cost the delay creates. Keeping them separate makes the follow-up clearer and avoids presenting an internal estimate as money the client owes.

SIMPLE INTEREST FORMULAbalance × annualized rate × chargeable days ÷ 365

A written flat fee is added only after the grace period. Your contract and applicable law—not this calculator—determine whether either charge is available.

Use the agreed terms

Enter the rate, grace period, and flat fee already stated in the governing agreement. Do not invent a new charge after the invoice becomes overdue.

Keep a calculation record

Save the balance, day count, annualized rate, interest, fee, and calculation date with the invoice. A reproducible number is easier to explain than a rounded demand.

Ask for a payment date

Keep the reminder factual: identify the invoice, state the overdue period and updated balance, then ask the client to confirm when the payment will arrive.

WORKED EXAMPLE

A 2,500 invoice that is 45 days overdue.

At an annual simple rate of 18% with no grace period or flat fee, the prorated charge is 55.48 and the updated balance is 2,555.48. A separate 12% internal cost-of-cash assumption values the delay at 36.99; that second number informs future pricing but is not added to the client balance.

IMPORTANT BOUNDARY

The calculator proves arithmetic, not entitlement.

Late-payment rules vary by agreement, location, client type, and transaction. Confirm the permitted basis before applying a charge, and seek qualified advice for a disputed or material debt.

13-STAGE INVOICE RECOVERY SYSTEM

Track the invoice. Send the next message.

The Invoice Recovery Pack pairs 13 calm-to-firm payment messages with a formula-driven 100-row tracker, aging dashboard, follow-up dates, promise-to-pay records, and an editable escalation cadence.

Get the Invoice Recovery Pack — $9 Get the free invoice follow-up starter

General planning information only—not legal, tax, or financial advice. Review contract language with a qualified professional for your jurisdiction and circumstances. Inputs stay in your browser; this site uses no analytics, cookies, or accounts. Open-source MIT code. Affiliate program.